Unravelling the diversity of the lichen genus Porina (Porinaceae) in Mauritius

Background and aims – Despite the publication of a recent checklist for Mauritius, a small archipelago in the south-western Indian Ocean, our knowledge of the lichen flora of this region remains incomplete. The present contribution is part of an ongoing study of lichen diversity of the islands of Mauritius and Rodrigues. It aims to unravel the diversity of the genus Porina s.l. on these islands and to improve the taxonomy and the phylogeny of the family Porinaceae following the morphological study and the sequencing of recently collected material.Material and methods – Lichens were collected in 2016 and 2019 in a range of environments, from lowland dry habitats up to dense evergreen upland forests on the islands of Mauritius and Rodrigues. In total, 85 samples of Porina were examined using light microscopy. A molecular study using mtSSU sequences was performed in order to investigate the phylogenetic position of the species of Porina occurring in the study area.Key results – The analyses revealed the presence of 23 species of Porina s.l. in Mauritius, while only four were previously accepted for this country. Five new species are described: Porina covidii, P. griffithsii, P. mauritiana, P. nuculoides, and P. rupicola, while two sterile species remain unidentified. The mtSSU phylogenetic tree includes 19 of the 23 species occurring in Mauritius. These species are dispersed throughout the phylogenetic tree, in at least eight main and strongly supported lineages, suggesting multiple colonizations of Mauritius. A new lineage only including Paleotropical and mainly foliicolous species (P. epiphylloides, P. longispora, P. mauritiana, and P. mazosioides) is revealed. Pseudosagedia crocynioides, a species that was previously known only from Florida, is newly reported from Mauritius, highlighting a remarkable disjunct distribution. Photos of each taxon are provided, along with an identification key to all species.Conclusion – The study of the genus Porina in Mauritius highlights a rich flora. The true diversity of Porina species in the south-western Indian Ocean is certainly underestimated and in need of further investigation, while a taxonomic-phylogenetic revision of tropical Porina at a broader geographical scale is highly desirable. The identity of several Mauritian specimens remains uncertain despite the use of molecular data.